1. Field of the Invention
The present invention relates to a magnetic head on which a magnetic tape slides with a pad pressing it so as to record or reproduce information on the magnetic tape, and to a method for manufacturing such a head.
2. Description of the Prior Art
In cassette tape recorders or the like, magnetic recording or reproduction of audio signals or the like is carried out on or from a magnetic tape during relative motion between the magnetic tape and a magnetic head. To maintain good and uniform contact between the magnetic tape and magnetic head, a pad for pressing the magnetic tape onto the magnetic head is disposed on a tape cassette.
The pad, on the one hand, improves the contact between the magnetic tape and magnetic head, but, on the other hand, it increases the sliding friction of the tape, which not only results in wow and flutter associated with tape speed instability, but also increases abrasion of the magnetic tape.
To overcome this problem, Japanese utility model application laying-open No. 63-91809 proposed the following technique to reduce the pressure of the pad on the magnetic tape: a pair of projections are disposed on the sliding surface of the recording head in such a manner that the magnetic tape passes between the projections, which are placed under the top and bottom portions of the pad.
FIGS. 1A and 1B are perspective views showing constructions of such magnetic heads for conventional cassette tape recorders.
As shown in these figures, a 2- or 4-channel magnetic core is provided in the center of a magnetic tape sliding surface 4 of a magnetic head 1. A magnetic tape 6 is pressed against this magnetic tape sliding surface 4, by a pad 15 shown by broken lines. The magnetic tape 6 moves in the direction indicated by the arrow A in FIG. 1B so as to slide on the magnetic core 5, thereby performing recording or reproduction.
In general, the magnetic tape sliding surface 4 is composed of a case 2 made of a metal, the windows of the case 2, the magnetic core 5, and a fixing member that fixes the above elements in their positions. A pair of rectangular projections 17 are disposed on the magnetic tape sliding surface 4 in such a manner that they are placed at either side of the magnetic tape 6, and are elongated like a band along the sliding direction A of the magnetic tape 6. The top and bottom portions of the pad 15 protruding beyond both sides of the magnetic tape 6 are pressed against the projections 17 with stronger pressure so that the pressure of the pad 15 against the magnetic tape 5 is reduced, thereby eliminating the above-mentioned problems.
The projections 17 on the sliding surface 4 are formed by the method, for example, disclosed in Japanese patent application laying-open No. 1-59605 (1989). In this method, a mask, which has mask windows at positions corresponding to the projections 17 on the magnetic tape sliding surface 4, is placed on the sliding surface 4. The projections 17 are formed by a method for physically forming films, such as metal spraying, vacuum evaporation, sputtering, electrodeposition, or the like.
The film formation, in general, is carried out after the magnetic tape sliding surface 4 has been subjected to mirror-like finishing. Owing to a sudden rise in temperature, this causes core deviation at the gap of the magnetic head at which the core ends are butted. This may result in deterioration in the contact between the magnetic tape 6 and the magnetic head 1, and may degrade the electromagnetic conversion characteristics of the head. Thus, when the projections 17 are formed by the metal spraying, vacuum evaporation, or sputtering, the speed of film formation cannot be increases beyond a certain limit, which hinders productivity.
In addition, metal spraying cannot form the film with sufficient precision, and hence the projections 17 must be initially made thicker than the desired thickness, and then undergo a precise finish cut in order to achieve the desired thickness, which is an extra process.
Furthermore, electrodeposition cannot be used to form a film on a resin material. Hence, when the projections 17 are formed by electrodeposition, they can be formed only on the metal portions and not on the fixing member, which is made of resin. This will unduly when the space between the projections 17, and hence the pad 15 cannot be positively positioned on the projections 17 when the magnetic tape 6 slides on the magnetic head. This may reduce the effect of the projections 17. In particular, in a 4-channel magnetic head, while the height of the window of the case is determined at 4.5 mm, that of the pad 15 is specified as more than 5 mm. Consequently, the dimensions of the top and bottom portions of the pad 15 which encounter the projections may be as small as (5.0-4.5)/2=0.25 mm. Considering the mounting looseness of the pad 15, it is easy to understand that the portions of the pad 15 positioned on the projections 17 are very unstable.
When the projections 17 are formed by metal spraying, vacuum evaporation, sputtering, or the like, films can be formed on the fixing member, and hence the above-described problem does not take place. However, the projections 17 may peel off from the fixing member because the adhesion between the projections 17 and the fixing member differs from that between the projections 17 and the metal portions, and because the adhesion between the resin and the film is inferior to that between the metal and the film.
Furthermore, the projections 17 thus formed are compressed owing to the difference between the temperature during film forming and the temperature thereafter, and so they may separate from the sliding surface 4. This is because the shrinkage stress of the projections 17 themselves acts after the projections have been subjected to the thermal changes during the formation thereof. Thus, undergoing changes in temperature and humidity with time, parts of the projections 17 may separate from the sliding surface 4, or the entire projection 17 may fall from the sliding surface 4. This will result in a considerable increase in the sliding friction or in wow and flutter.
Incidentally, the running position of the magnetic tape 6 on the magnetic sliding surface 4 of the recording head 1 is regulated in various ways, conventionally.
FIG. 2 is a perspective view showing the construction of a conventional magnetic head device having a tape guide portion. In FIG. 2, each of two tape guides 21 has tape contact surfaces 22 which are uprightly disposed in the crosswise direction of the magnetic tape 6 so as to make contact with both sides of the magnetic tape 6. The tape contact surfaces 22, making contact with both sides of the tape 6, regulate the running position of the tape 6.
The magnetic head device of FIG. 2, however, has the problem that the tape 6 may curl in the vicinity of the tape contact surfaces 22 when the tape 6 snakes. In general, to prevent this and the electromagnetic conversion loss caused by the space between the tape 6 and the magnetic gap G on the magnetic tape sliding surface 4 of the head, the tape 6 is pressed to the magnetic tape sliding surface 4 of the magnetic head by the pad 15 disposed in a tape cassette 36 as shown in FIG. 3. The curl of the tape 6, however, cannot to prevented if the tape 6 snakes substantially. Thus, the electromagnetic conversion loss due to the space may increase, or the tape running position may shift by an amount corresponding the curl. This will result in tracking failure and a sharp deterioration in the electromagnetic conversion characteristics of the magnetic head, particularly for a 4-channel recording and reproducing head as shown in FIG. 2.
To improve the running problem of the magnetic tape 6, a magnetic head device has been proposed which has a tape guide portion which can stabilize the electromagnetic conversion characteristics.
FIG. 4 is a perspective view showing the construction of a conventional magnetic head device of such a type. As shown in this figure, each of the two tape guides 21 has a tape contact surface 22 which is uprightly disposed as a reference surface for regulating the position of the tape 6 by keeping contact with one side of the tape 6. Each of the two tape guides also has a curved sliding portion 23 for regulating the position of the tape 6 in the direction of the thickness thereof by keeping contact with the bottom of the tape 6, and an inclined portion 24 for forming an inclined surface with which the other side of the tape 6 makes contact.
With this arrangement, the other side of the tape 6 is pressed to the inclined portion 24 by setting the space between the tape contact surfaces 22 and the inclined portion 24 smaller than the width of the tape 6 which keeps contact with the curved sliding portion 23. This will increase the tension acting on the tape 6, which in turn presses the tape 6 to the tape contact surfaces 22, and hence the tape 6 runs while being pressed to the tape contact surfaces 22. Thus, the running position of the tape 6 will be positively regulated so that a deterioration in the electromagnetic conversion characteristics can be effectively prevented.
In the magnetic head device in FIG. 4, however, it has been found that once the tape 6 has snaked, it takes a very long time to restore the running position of the tape 6 to its normal position. The reason for this is as follows:
FIG. 5 is a cross sectional view, taken along line a--a' of FIG. 4, showing the vicinity of the magnetic gap G of the magnetic head device to illustrate the tape running state at the major portion thereof. FIG. 5 is vertically enlarged to make the tape running state clearer.
As shown in FIG. 5, the tape 6 is pressed against the tape sliding surface 4 of the magnetic head 1 by the pad 15. Here, the thickness of the tape 6 is usually 12-18 .mu.m, and hence the pad 15 will be greatly deformed at both sides of the tape 6. Thus, the stress caused by the pad 15 will concentrate on both sides of the tape 6, and the pad 15 also presses the tape sliding surface 4.
If the tape 6 snakes in such a condition, the tape tension increases owing to the inclined portions 24 of the guides 21 so that a force to restore the tape 6 to its normal position is produced. The force, however, is hindered from acting because the stress of the pad 15 concentrates on both sides of the tape 6, and the deformation of the pad 15 exerts pressure on the tape sliding surface 4. As a result, in the magnetic head device shown in FIG. 4, once the tape 6 has deviated from the normal running position, it takes very long time until the tape 6 is restored to its normal position.